1. Technical Field
The present invention relates to a radio communication system technology in an interworking system between a mobile communication network and a wireless LAN that enables communications over a mobile communication network and a wireless LAN performed by a terminal having interfaces to both of the communication networks to be optimally allocated between the networks.
2. Background Art
Engineers are working to build a communication system that allows mobile phones capable of communicating in a wide area to interwork with a public wireless LAN service which enables fast data communication in a relatively small area to complement each other. In such a communication system, the following service, for example, can be provided by using a terminal capable of accessing both mobile phone network and wireless local area network (WLAN). A terminal uses a mobile communication network in which an area covered by each base station is wide to maintain connection while the mobile phone is moving fast whereas the terminal uses a wireless LAN to make fast access while the terminal is moving slowly or is stationary.
The interworking system is standardized by the 3GPP (3rd Generation Partnership Project). The 3GPP has standardized an architecture in which a scenario for accessing a packet service provided by a mobile network through a Wireless Local Area Network (WLAN), for example. 3GPP specifications are a new worldwide standard for creation, delivery and playback of multimedia over third-generation fast wireless networks. In 3GPP specifications, TR (Technical Report) 22.934 describes requirements of interworking systems, TS (Technical Specification) 23.234 (see 3GPP TS23.234 “3GPP system to Wireless Local Area Network (WLAN) interworking; System description”) describes an architecture, and TS33.234 describes an authentication method.
In these interworking system specifications, six scenarios, Scenarios 1 to 6, are defined for different interworking forms. For example, in Scenario 3, a service is defined that enables a terminal in an area covered by a wireless LAN to access a mobile communication network. In Scenario 4, a service is defined that enables a terminal to maintain an ongoing communication session when the terminal moves between a wireless LAN coverage area and a mobile communication network coverage area during communication.
One method for implementing Scenario 4 by using an existing technique is to combine Mobile IPv6 with a 3GPP interworking system. Mobile IPv6 is specified by RFC 3344 of the IETF (Internet Engineering Task Force) (see IETF RFC 3344, “IP Mobility Support for IPv4”). The aim of this technology is to hide movement of a terminal from the other party's terminal by using Mobile IPv6. This enables the terminal to maintain an ongoing communication session when the terminal moves between a wireless LAN and a mobile communication network.
FIG. 19 is a diagram for outlining a configuration of a system which is a combination of a Mobile IPv6 and a 3GPP interworking system. In FIG. 19, reference numeral 1901 denotes a terminal, which corresponds to UE (User Equipment) in 3GPP. The terminal 1901 includes interfaces for a wireless LAN and a mobile phone network and is connected to a mobile (communication) network 1902 and a wireless LAN 1903. The mobile network 1902 includes a mobile access network 1904, a packet controller 1905, and a mobile network packet gateway 1906. The wireless LAN 1903 includes a WLAN access network 1908, a WLAN gateway 1909, and a packet data gateway 1910.
The mobile access network 1904 provided in the mobile network 1902 is capable of communicating with the mobile phone of the terminal 1901. The mobile access network 1904 corresponds to UTRAN (Universal Terrestrial Radio Access Network) of 3GPP. The packet controller performs GPRS (General Packet Radio Service) connection setup for the terminal 1901. The packet controller 1905 corresponds to SGSN (Serving GPRS Support Node) of 3GPP. The mobile network packet gateway 1906 corresponds to GGSN (Gateway GPRS Support Node) of 3GPP. The mobile network packet gateway 1906 relays packets between the mobile network 1902 and a public packet-switched network 1911.
The WLAN access network 1908 provides a wireless LAN connection to the terminal 1901. The WLAN access network corresponds to WLAN AN (Access Network) of 3GPP. The WLAN gateway 1909 is connected to the WLAN access network 1908 and relays packets that have access to the mobile network 1902. The packet data gateway 1910 relays WLAN packets to the public packet-switched network 1911. The public packet-switched network 1911 is connected to the mobile network 1902 and the wireless LAN 1903 and performs packet switching in the public packet-switched network 1911. The public packet-switched network 1911 corresponds to PDN of 3GPP.
An IMS server 1907 controls an IMS (IP Multimedia Core Network Subsystem) which connects the mobile network packet gateway 1906 to the packet data gateway 1910 and supports realtime communications on a packet-switched network. The IMS server 1907 corresponds to P-CSCF (Proxy-Call Session Control Function) of 3GPP. A user information storing device 1912 manages the connection status of the terminal 1901. The user information storing device 1912 is connected to an authentication system 1913. The authentication system 1913 relays signals for authentication between the user information storing device 1912 and the WLAN gateway 1909 when authentication requested from a wireless LAN is performed. The user information storing device 1912 corresponds to both of AAA Proxy and AAA Server of 3GPP.
Connected to the public packet-switched network 1911 are a home agent 1914 and a correspondent node 1915. The home agent 1914 is a home agent of Mobile IP. The correspondent node 1915 communicates with the terminal 1901.
The following provides an overview of operation of the communication system shown in FIG. 19. When the terminal 1901 is powered on, the terminal 1901 first registers the position of itself and enters the standby state. At this point of time, the terminal 1901 obtains an access IP address for accessing the mobile network 1902 and registers the home IP addresses of the terminal and Mobile IP with the IMS server 1907.
The access IP address IPa is an IP address used when the terminal 1901 accesses the public packet-switched network 1911. When the terminal 1901 uses the mobile network 1902, the mobile terminal 1901 obtains an access IP address through the mobile network packet gateway 1906. When using the wireless LAN 1903, the mobile terminal 1901 obtains an access IP address through the packet data gateway 1910. Since the mobile terminal 1901 is located in an area (M1) covered by the mobile network 1902 in the example shown in FIG. 19, the mobile terminal 1901 obtains the access IP address IPa through the mobile network packet gateway 1906.
After obtaining the access IP address, the mobile terminal 1901 uses the access IP address IPa and the home IP address IPc to register its position with the home agent 1914. For the position registration, the mobile terminal 1901 may holds its unique home IP address IPc or a functional element of the network may assign the home IP address IPc. After completion of the position registration, the terminal 1901 registers an ID (IMSI: International Mobile Subscriber Identifier) of the terminal 1901 and the home IP address IPc with the IMS server 1907. The position registration processing is thus completed.
Then, the terminal 1901 waits for a call. An example will be described here in which, after the mobile terminal 1901 enters the wait (standby) state, the mobile terminal 1901 sends a signal using IMS to start a video telephone call which is a combination of audio and video. The audio and video streams are transmitted through the home agent 1914 and the mobile network packet gateway 1906.
When the terminal 1901 enters an area (L1) of the wireless LAN 1903, packets are transmitted to the mobile terminal 1901 over the wireless LAN 1903. An overview of a handover process for making this switching will be given below. When the mobile terminal 1901 enters a cell L1, the mobile terminal 1901 obtains an access IP address IPb for accessing the wireless LAN 1903. Then the terminal 1901 performs Mobile IP registration with the home agent 1914 in order to perform communication over the wireless LAN 1903. The home agent 1914 updates information concerning communication by the terminal 1901 so that packets are routed through the packet data gateway 1910.
With the process described above, the home IP address IPc used by the home agent 1914 appears to remain unchanged to the correspondent node 1915 when the terminal 1901 moves from the mobile network (M1) to the wireless LAN (L1) during communication. Because the home IP address IPc has been registered, it no longer needs to be registered with the IMS server 1907.
Japanese Patent Application Laid-Open No. 2004-180311 discloses a method for connecting a terminal device to a router in a radio communication network. In the method, the terminal device uses a first network interface to establish a link-layer connection with a first access point, then uses a second network interface to detect a second access point and establish a link-layer connection with the second access point. Then determination is made as to whether the terminal device is compatible with a connection router connecting to the second access point before the terminal device is connected to the connection router.
FIG. 20 is a conceptual diagram for illustrating the method disclosed in Japanese Patent Application Laid-Open No. 2004-180311 described above. In the system shown in FIG. 20, a mobile network 2002 interworks with a wireless LAN 2003, as with the system shown in FIG. 19. A mobile network packet gateway 2004 is provided in the mobile network 2002 and an LMA (Local Mobility Agent) 2005 is provided in the wireless LAN 2003. Functional elements relating to radio communication such as a radio network controller (RNC) are not shown. Basic operation of a terminal 2001, the mobile network 2002, and the wireless LAN 2003 shown in FIG. 20 is the same as that of the system in FIG. 19 and a public packet-switched network 2007 and a correspondent node 2008 are also the same as the public packet-switched network 1901 and the correspondent node 1915 of FIG. 19. Therefore, overlapping description of these will be omitted.
Like the mobile network packet gateway 1906 shown in FIG. 19, the mobile network packet gateway 2004 relays packets and manages connection of the terminal 2001. The LMA 2005 relays packets between the mobile network 2002 and the wireless LAN 2003 and assigns an access IP address in response to a request from the terminal 2001. An ISP (Internet Service Provider) 2006 provides connection to the public packet-switched network 2007 and assigns an IP address to the terminal 2001.
In the system shown in FIG. 20, when the terminal 2001 is powered on, connection of the terminal 2001 to the public packet-switched network 2007 is established. The terminal 2001 uses a GPRS procedure to obtain an IP address IP-mt and generates connection information called “Secondary PDP context” for a GGSN. The “Secondary PDP context” is connection information on GPRS connection such as QoS. Relay information in the connection information can be used for the wireless LAN as well.
When the terminal 2001 enters an area of the wireless LAN 2003, the terminal 2001 obtains an access IP address for accessing the wireless LAN 2003 and performs Mobile IP registration with the LMA 2005. The LMA 2005 uses GPRS to perform registration with the mobile network packet gateway 2004. As a result, the LMA 2005 of the wireless LAN 2003 is associated with the connection information on the terminal 2001 and packets of the terminal 2001 are transferred through the LMA 2005.
Packets directed to the terminal 2001 are transferred through both of the mobile network 2002 and the wireless LAN 2003 at the same time in the system shown in FIG. 20. This can distribute the load across the networks when traffic concentrates one of the networks.